Add assertion for TS version

[danvk]

This text in the preface of Effective TypeScript could be checked:

All samples were verified with https://github.com/danvk/literate-ts[literate-ts] using TypeScript 5.3 beta.

Maybe something like:

All samples were verified with https://github.com/danvk/literate-ts[literate-ts] using TypeScript 5.3 beta.
// verifier:assert-ts-version-in-preceding-paragraph

And this would ensure that "TypeScript 5.3 beta" appears somewhere in that paragraph.

This might make testing new versions annoying.